Regulator-meter utilizing a beam of light for indication and regulation

ABSTRACT

Regulator-meter apparatus includes signal-responsive meter mechanism for projecting a light spot onto a transparent screen such that the spot traverses the screen during signal-caused movement of the mechanism. The position of the spot on the screen is detected by two photosensitive elements which define one set point for the regulator portion of the apparatus, the elements being spaced apart a distance slightly greater than the corresponding cross-sectional dimensions of the spot and having the outputs thereof connected to different ones of the set and reset inputs of a bistable multivibrator. The bistable assumes either its set or reset state depending upon the position of the spot relative to the elements. Circuitry is provided for effecting initial full-scale energization and de-energization of the mechanism, causing the bistable to assume a known initial state, for example, the reset state. The cross-sectional shape of the spot is defined by a suitably apertured mask, mounted so as to be responsive to the displacements of both a proportionaleffect and an integral-effect bimetallic element.

United States Patent Dumast et al.

[ 51 Sept. 19, 1972 [54] REGULATOR-METER UTILIZING A 3,337,739 8/1967Sendro ..250/231 BEAM OF LIGHT FOR INDICATION 3,309,498 3/ 1967 Nagy..250/231 AND REGULATION 3,349,245 10/1967 l-losker ..250/231 [72]Inventors: Michel Dumast, Pantin; Guy Rou- Primary Examiner jamesLawrence 9 5 Luc Assistant Examiner-D. C. Nelms Thevenin,Comerlles-en-Pansrs, all Atwmey wmiam R Sherman of France 1 [73]Assignee: Societe DInstrumentation Schlum- [57] ABSTRACT I berg", ParisFrance I Regulator-meter apparatus includes signal-responsive [22]Filed; Sept 3, 1970 meter mechanism for projecting a light spot onto atransparent screen such that the spot traverses the 1 1 pp NOJ 69,294screen during signal-caused movement of the mechanism. The position ofthe spot on the screen is Related Application Dam detected by twophotosensitive elements which define [62] Division of Ser. No. 841,695,July 14, 1969, one s t point for the regulator portion of the ap- Pat.No. 3,606,151. paratus, the elements being spaced apart a distance Islightly greater than the corresponding cross-sectional 52 us. Cl...250/230, 250/231, 324/97 dimensions of the Spot and having the Outputsthereof [51] Int. Cl. ..G0ld 5/30 Connected different Ones of the Setand reset inputs 5 Field f Search 250 230 2 3 23 59; 324 9 of a bistablemultivibrator. The bistable assumes either 324/97 110; 317/127; 340/2155 its Set or reset state depending upon the position of the spotrelative to the elements. Circuitry is provided 56] References Cited foreffecting initial full-scale energization and de-energization of themechanism, causing the bistable to as- UNITED STATES PATENTS sume aknown initial state, for example, the reset state. The cross-sectionalshape of the spot is defined 3,271,677 9/1966 Peter ..250/230X by asuitably apertured mask, mounted so as to be 3,271,754 9/ 1966 Corbell..250/230 X 3 025 038 3/l962 McDuffie 250/230 responsive to thedlsplacements of both a propor t a l t d al a t all I 3,054,928 9/1962Schrenk ..250/231 anmtegr ec b'met e emem 3,028,503 4/1962 Stevenson..250/231 3 Claims, 2 Drawing Figures 12 1s 30 44 e I 22" 5 52 1, 33 J1e 3e 1 PATENTED SEP 19 I972 SHEET 1 0F 2 INVENTORS Michel Dflmasf GuyRouzaqd Luc Thevenm PATENTED SEP 19 I972 sum 2 or 2 BISTABLE BIASCIRCUIT REGULATOR-METER UTILIZING A BEAM OF LIGHT FOR INDICATION ANDREGULATION This application is a division of US. application Ser. No.841,695, filed July 14, 1969 now US. Pat. No. 3,606,151.

This invention relates to control apparatus and more particularly to aregulator-meter for measuring and controlling the temperature ofindustrial equipment, such as an oven.

Regulator-meters for controlling industrial equipment typically measurea parameter such as temperature, pressure or flow and maintain thisparameter in the vicinity of some predetermined value or set point.These regulators are often used to control ovens and the like in whichthe temperature must be held substantially constant and equal to somepredetermined value.

The meter portion of the regulator-meter generally includes agalvanometer to which is applied 'a voltage proportional to theparameter to be measured. The moving coil of the galvanometer drives apointer, which typically mounts a flag or mask at the free end thereof;the mask moving along a front scale bearing suitable indicia uponrotation of the pointer. A detecting system gives a yes-or-no signalaccording to whether the position of the flag is to the left or to theright of the set point. This signal actuates a relay which may beconsidered as part of the regulator portion of the regulatormeter byreason of its more direct interface with the means for regulating anassociated apparatus (an oven, for example). Various conventional typesof systems, which may be photoelectric, capacitative or indicative innature are currently used to detect the position of the flag. FrenchPat. No. 1,330,847, is exemplary of a system which is basicallyindicative in nature in that it employs a metallic flag movable betweentwo oscillating coils placed at the set point to change the LC timeconstant and hence the frequency of coil oscillation. A change in coilfrequency is detected to provide an indication of the position of theflag.

However, disadvantageously these pointer systems are relatively fragileand since the pointers rotate about a central axis, usually requirearcuate front scales. Furthermore, the pointer and the flag have arelatively high inertia which reduces the speed or response of thegalvanometer.

Projectedlight type meters, on the other hand, do not have suchdisadvantages. Instead of employing mechanical pointers, projected lightmeters commonly use a light spot, that is, a concentrated beam of light,reflected from a mirror mounted to rotate with the moving coil of thegalvanometer. Unfortunately, the use of a light spot for regulationpurposes gives rise to numerous problems. One such problem is thatalthough it is a relatively simple matter to detect the passage of thespot at the set point, for example, by means of a photoelectric celllocated at the set point, it is a far more difficult proposition todetermine if this light spot is to the right or to the left of the setpoint after movement.

Further, for the meter to be wholly reliable, it is also necessary toprovide numerous safety measures. For example, should there be a failureof the lamp filament, momentary failure of the power supply or breakageof the sensor associated with the controlled equipment, the regulatormust react so as not to give erroneous commands which might damage theequipment. These problems, which did not occur with a moving vane, havenot been satisfactorily solved for meters employing moving light spots.

An object of the invention is to provide a regulatormeter without thedisadvantages mentioned hereinabove, using a light spot both forindication and regulation.

Another object of the invention is to provide a regulator-meterincluding a simple light spot detection system which allows one to knowat any time, if the light spot is to the right or to the leftof a setpoint.

A still further object of the invention is to provide a regulator-meterutilizing a movable light spot rather than a movable pointer, with allthe safety features needed for reliable operation.

According to the instant invention, a regulator-meter includes a mirrorgalvanometer for projecting a light spot onto a transparent screen, thelight spot traversing the screen along a defined path upon rotation ofthe mirror. The position of the light spot is detected by twophotoelectric elements which are located along the path of the spot. Twosuch elements define one of the regulator set points. The outputs ofthese two cells are respectively connected to the set and reset inputsof a bistable device. The bistable takes either one or the other of twocorresponding stable states when the light spot is resting on one sideor the other of the cell photosensitive element. A sweeping orfull-scale electrical signal is applied to and then removed from thegalvanometer when the unit is switched on initially in order to triggerthe bistable so that it always assumes the same initial state, forexample, the reset state.

It is also known in the prior art to transform an operatingregulator-meter, which may be described as a yes-no" or go-no go type,into a proportional effect regulator by using a modulating bimetallicelement heated simultaneously by an intervening component, such as amotor, heating resistor or pump. The oscillations of the regulatedparameter around its set point are then considerably reduced. Inpractice, the proportional effect bimetallic element moves the set pointso that the regulator oscillates about an average frequency whichdetermines the proportional regulation range. Such a control for atemperature-regulated oven is especially typical.

In the proportional regulation range, heating of the oven and of thebimetallic element is established during intervals, the duration andfrequency of which depend upon the amount and speed of deflection of thebimetallic element and on the heating and cooling speeds of the oven.Generally speaking, the extreme points of the sweeping range of thebimetallic element are designated to be symmetrical relative to the setpoint. Fast heating ovens stabilize at a temperature very close to theupper limit of the regulation range and hence the effective heating timeintervals are very short, at least compared to the oven-cooling timeconstant. Slow heating ovens, on the contrary, stabilize at atemperature close to the lower limit of the proportional regulationrange, the effective heating time intervals being interrupted only for ashort time. Between these two extreme cases, all intermediate cases are,of course, possible.

To cancel the permanent systematic error due to proportional effectregulators, it is known to add an integral correction system. Anintegral correction bimetallic element may be used, the heating andcooling time constants of this second bimetallic element being generallycomparable to those of the oven and, in any case, long compared to theconstants of the proportional effect bimetallic element. Such systemsare described, for example, in French Pat. Nos. 1,222,293 and 1,223,299.The effects of proportional and integral effect bimetallic elements areopposed and inasmuch as the integral action bimetallic elementintegrates the successiveheating intervals given by the modulationbimetallic element, the sweeping range of the modulation bimetallicelement is offset by a value proportional to the average energy appliedto the oven so that the true and set temperatures are driven toward, andfinally to, equality.

In the apparatus described in the patents mentioned hereinabove, theproportional and integral effect bimetallic elements vary the positionof the set point. However, this design is physically implemented byrelatively complex and fragile mechanical systems which it would bedesirable to simplify.

Therefore, a still further object of the invention is to provide anuncomplicated assembly of proportional and integral effect bimetallicelements which utilize to advantage a light spot and photoelectricdetecting cells.

According to this aspect of the invention, the light spot comprises areading spot and a regulating spot. The reading spot is obtained by anaperture extending therethrough configured to shape incident light intoa reading spot of desired cross-section, the mask being attached to themeter movement. The regulating spot is obtained by a regulation maskmounted on the end of a proportional effect bimetallic element. Theproportional effect element is associated with an integral effectbimetallic element synchronously heated with said proportion effectelement, the deflections of said elements being opposed to each otherand the integral effect element having a long thermal time constantcompared to the proportional effect element.

As a result of the instant arrangement of integral and proportionaleffect elements, the manufacture of light sp'ot indicator-regulatorspossessing both effects is made particularly easy. The cells whichdetermine the set points, after their initial positioning, need not besubsequently adjusted and the relatively complex and fragile mechanismwhich, up to now, has been used both for adjusting and causingoscillations at the set point is considerably simplified by separatingthe functions and using an adjusting mechanism for the cells and anoscillating mechanism for the regulation mask.

The characteristics and advantages of the invention will be furtherenhanced by the description to follow which is given solely as anon-limitative example with reference to the attached drawings on which:

FIG. I is a perspective view of a regulator-meter according to theinvention showing the inner layout of the various components; and

FIG. 2 is a diagram of the electrical circuits used in the meter shownin FIG. 1. 7

Referring to FIG. I, a regulator-meter comprises a housing of overallrectangular shape having sidewalls 2 and a rectangular cover 4 mountedthereon. The housing front wall 6 mounts a flat translucent screen 8inscribed with scale indicia l and the housing rear wall 12 mounts aincandescent lamp 14. A condensing lens 16 is mounted in front of thelamp 14 to focus visible light rays emanating from the lamp 14 onto twomasks l8 and 20. Mask 18 is attached to a sidewall of housing 2 andincludes a triangular-shaped aperture 22. Mask 20, located approximatelyin the same plane as the mask 18, has a rectangular-shaped aperture 24extending therethrough and is mounted fixedly on the free end of a firstbimetallic element 27 of overall rectangular shape and having amidlength section surrounded by a heating resistor 27. Bimetallicelement 26 is attached to a spacer 28 which mounts a heat insulatedplate 29 composed of asbestos, for example, and a small metal block 30formed with a central bore in which is placed a heating resistor 31, theresistor 31 being electrically insulated from the block 30 byencapsulating in a material of. relatively low heat conductivity, forexample, ceramic. The block 30 is fixedly mounted to a second bimetallicelement 32, similar to the element 26, and attached to the sidewall 2.The assemblies of bimetallic elements 26 and 32 are such that theydeviate in opposite directions when heated. The time necessary for thebimetallic elements to be completely deflected under the effect of theirrespective heating resistors 27 and 31 are, for example, approximatelyone and five minutes respectively. Adjacent to, and in optical alignmentwith, the aperture 22 is a dual-color transparent filter 33, having, forexample, a red filter section 34 and a green filter section 36 joinedtogether in endwise relationship. The filter 33 is attached fixedly to ametal plate 38 which can pivot between two positions around a pivot pin40 in directions perpendicular to the plane of filter 33. The positionof the plate 38 is controlled by a solenoid 42.

The light originating from bulb 14, after having passed through lens 16,slots 22 and 24 and filter 33 strikes a planer, reflective mirror 44inclined to incident rays of light 52 so as to reflect such lightthrough a further condensing lens 46. Light rays 54 leaving the lens 46are directed onto a mirror 48 mounted on the moving coil of a'galvanometer 50 and form a colliminated beam of light spot 58 on thefront wall 6 of housing 2. .The focal distance of lens 46 is selected soas to provide a clear image of the luminous object formed by aperture 24and triangular aperture 22. It will be noticed that the image isinverted relative to the luminous object, the triangular part 60 orindicating spot striking the translucent screen 8, and the elongatedpart 6, or regulating spot, impinging upon an opaque region beneath thisscreen, that is, on the opaque part of front surface 6. Galvanometer 50is conventional with a moving coil 64 and magnetic parts 66. A carriagemay be moved along a slideway 68 parallelto front surface 6 and locatedimmediately behind this surface, this carriage 70 having twophotoelectric cells 72 and 74 mounted thereon. These two cells have theshape of two narrow, vertically oriented rectangles spaced apart adistance slightly less than the width of the regulation spot 62. Avertical axis located centrally or midway between these two cellsrepresents the position of the set point for regulation, this axis beingmaterialized by a pointer (not shown) attached to carriage 70 andlocated in front of translucent screen 8.

FIG. 2 shows the various electrical circuits of the in dicator regulatorshown in FIG. 1, used for example,

for measuring and controlling the temperature of an electrical oven 80heated by a resister 82. The temperature of the oven is sensed by athermocouple 84 connected to the regulator-meter. Other temperaturesensors such as resistor sensors may be used in lieu of the thermocouple84.

The regulator-meter is supplied with A.C. current applied to atransformer 86 with three outputs. The first output is applied to thelamp 14. A resistor 88 con nected in series with lamp 14 has itsterminals connected to a bias circuit 90. The second output oftransformer 86 is connected through a switch 92 to the heating resistors27 and 31 connected in series. The coil of electromagnet 42 is connectedin parallel to these two heating resistors 27 and 31. The third outputof transformer 86 is connected to a direct current power supply 93 theoutput of which is connected to a bistable flip-flop 94 through a switchshown in the form of a transistor 96. The base of transistor 96 isconnected to the output of bias circuit 90. Bistable 94 includes setterminal S connected to the photoelectric cell 72 and also referred toas C1, and a reset terminal R connected to the photoelectric cell 74also referred to as C2. A third cell 98 referred to as C3, is alsoconnected to the terminal R, the three cells being supplied with DC.voltage from supply +V. The output signal from bistable 94 is applied tothe coil 112 of an electromagnetic relay controlling a first set ofcontacts 114 connected in series with the oven heating circuit 82 and asecond set of contacts 92, connected as described hereabove.

A relay 114 is controlled directly by the bistable 94. It is thuspossible to interpose, between this bistable and the coil of relay 112,a control circuit of the type described in applicants French patentapplication PV l4l,329, filed Feb. 27, l968and entitled anElectromagnetic Relay Control System.

The thermocouple 84 is connected for sensitivity adjustment throughresister 100 to the terminals of the galvanometer 50, a resister 102representing the lead resistances. The galvanometer 50 is also connectedby means of a sweeping pulse circuit 104 to DC. voltage delivered bysupply 93, this voltage being taken off the collector of transistor 96.The sweeping pulse circuit 104 includes a differentiating circuit formedby capacitor 106 and a resistor 108 followed by a buffer-amplifier 110.The purpose of circuit 104 is to deliver to the galvanometer 50 asweeping pulse every time the supply 93 is switched on. The reasons forgenerating this sweeping pulse are explained in greater detailhereafter.

The DC. voltage produced by the supply .93 is also supplied by means oftwo conductors 118 and 120 to the input terminals of thermocouple 84.Conductor 118 incorporates a resistor 116 of high resistance value. Thecircuit formed by conductors 118 and 120 and resistor 116 cooperateswith the photoelectric cell 98 to stop heating of the oven in case thethermocouple 84 is broken, as will be explained subsequently.

In operation, thermocouple 84 generates a voltage which is a function ofthe temperature of the oven 80 and the deviation of the galvanometerspot is proportional to this temperature. It will, firstly, be assumedthat the oven is being heated and that its temperature is lower than theestablished set point. Luminous spot 58 is therefore to one side of thecells C1 and C2. Bistable 94 is in the active state and, therefore,closes switch 114. As the temperature of the oven increases the spot 58moves toward the right (assuming the observator looks at the frontscreen 8). When the regulation spot 62 encounters cell C1 connected tothe set terminal of bistable 94, nothing happens since this bistable isalready in the active state. On the other hand, when spot 62 encounterscell C2, bistable 94 returns to the passive or reset state and relay I14opens, thereby stopping the heating of the oven. Conversely, when thetemperature of the oven decreases, spot 62 returns towards the left andby traversing the cell Cl triggers bistable 94 into the active state,thereby closing switch 114. When the balanced temperature of the oven isobtained, the spot lies between the two cells C l and C2. Since thespacing between the cells is very slightly less than the width of thespot the latter are permanently sensitized and a slight movement towardsthe right stops the heatingand a slight movement towards thepassivestate characterized by a Obit potential level on its logical 1 outputterminal and its set state as an active state characterized by a 1 bitlevel on its logical 1 output terminal. In this manner, if a momentaryopen circuit or other failure occurs in the mains or other power supplyfailure occurs, when the temperature of the oven is greater than the setvalue, the switches 92 and 114 will remain open during the period thepower supply is reestablished since the bistable will then return to thepassive state. If the oven is cold when the indicator regulator isswitched on, the bistable, therefore, remains in the passive state andthe oven does not heat up. To avoid this disadvantage, the sweepingpulse circuit 104 is provided. When the DC. voltage delivered by thepower supply 93 rises from zero volts to its normal level, thedifferentiating circuit formed by capacitor 106 and resistor 108produces a well-defined pulse which is applied through buffer amplifier110 to galvanometer 50. In response to this pulse, the spot 58 sweepsscale 10 up to maximum or full scale position and then returns to itsnormal operational position. During this sweeping operation, regulatingspot 62 energizes, successively, cells C1 and C2 and then in reverseorder C2 and Cl, if the temperature of the oven is less than the saidtemperature. The bistable 94 successively enters the active state whenthe spot passes over the cell C1 and to the passive stage when the spotpasses over the cell C2. 011 return, nothing happens when the spotpasses C1; the bistable 94 returning to the active state when this spotpasses over C1. This is therefore the desired heating position. Thissweep happens in the same manner when a momentary power failure occurs,thereby closing switch 114 when the current is re-established if thetemperature of the oven is less than the set point value.

Polarization circuit 90, resistor 88 and transistor 96 form a safetysystem in case of breakage of the filament of lamp 14. If this failureoccurs, the difference in potential between the terminals of resistor 88becomes null, circuit no longer supplies the bias voltage to the base oftransistor 96 which thereupon stops conducting. Since coil 112 is nolonger supplied current switch 114 opens and terminates the heating ofthe oven.

When the oven 80 starts heating, the contact 92 of relay 112 closes andpower is applied to heating resistors 27 and 31 of the proportional andintegral effect bimetallic elements 26 and 32, respectively. Thedirection of deflection of the element 26 is such that mask 20, which iscarried by said bimetallic element, is offset relative to the readingspot 60, which always indicates the true value of the temperature. Thedirection of deflection of the element 32 is opposite to that of theelement 26 so that the regulation range is constantly offset by a valueproportional to the average energy applied to the oven and that the trueand set temperatures are identical under stable operating conditions.

It can be seen that the mechanical assembly of elements 26 and 32 isparticularly simple, rugged and inexpensive. The same is true for thecells C1 and C2.

The switch 92 also controls solenoid 42 which controls the position ofthe two color filters 34 and 36 relatively to the opening 22. Duringheating of the oven, the solenoid pulls in that the green filter 36 ismoved in front of the opening 22 and as a result a green reading spot 60appears on the screen 8. Above the set value that solenoid pulls out andthe filter 33 is pivoted until the red filter 34 moves in front of theopening 22 whereupon the reading spot 60 becomes red. This system makesit possible for the operator to ascertain, at a glance if and how thesystem is operating.

Conductors 118 and 120, resistor 116 andthe third photoelectric cell 98combine to form a safety device in case of breakage of the thermocouple84. Cell 98 is mounted behind the front wall 6 in front of the zero ofgraduation (FIG. 1). Without this safety system, should thermocouple 84break, the spot would return to the mechanical zero and the oven wouldremain in heating position even at high temperatures. The direct currentpower supply, therefore, is applied to the terminals of the thermocouplethrough resistor 116. If thermocouple 84 is not broken, the additionalvoltage applied to galvanometer 50 by conductors 1 l8 and 120 isnegligible because the value of resistor 116 is very high compared tothe internal resistance of thermocouple 84. The measurement, therefore,is not affected. On the other hand, if the thermocouple is defective,all the power supply voltage is applied to the galvanometer. Conductors118 and 120 are connected in such a manner that when this voltage isapplied, the spot 58 deviates towards the left. Regulation spot 62impinges on photoelectric cell C2 which places bistable 94 in thepassive state, thereby cutting the heating of oven 80. This safetysystem operates for low impedance sensors. If a sensor of the variableresistance type is used, this safety system can be deleted sincebreakage of the sensor would result in unbalance in the measuring bridgewhich would give a deviation of the spot towards the maximum reading ofthe scale, thereby stopping the heating. In this case, the cell C2 canalso be placed beyond the scale number representing the maximum value ofinterest.

The regulator-meter although described as being used to control thetemperature of an oven, could, of

course, be used to regulate other types of apparatus re uirin a es ornot e re ulation.

%Vhat%s c aimed is: yp g 1. Apparatus comprising, a viewing medium,means for directing a light beam onto said medium for viewing, meansresponsive to beam radiation for producing an output electrical signal,a utilization device, bistable means coupled to said means responsive tobeam radiation and responsive to said output signal to change state forcontrolling said utilization device and means for driving said means fordirecting through a predetermined initial cycle to drive said bistablemeans into an initial, predetermined state.

2. Apparatus comprising, a light-transmitting medium, optical meansdrivable by a signal under measurement for projecting a beam of lightonto said medium, the driving of said optical means causing said beam tosweep said medium along a path, means located at a predeterminedposition on said path for producing an output electrical signal inresponse to incident radiation from said beam, bistable means coupled tothe signal-producing means and changing state in response to said outputsignal, means for driving said optical means with a signal ofpredetermined magnitude sufficient to displace said beam past saidsignal-producing means at least once, whereby said bistable means iscaused to assume a predetermined initial state.

3. The apparatus as claimed in claim 2 wherein the signal producingmeans comprises, two photoelectric elements spaced apart along said patha distance slightly greater than the corresponding cross-sectionaldimension of said beam, the region between said two elements defining aset point for the apparatus.

1. Apparatus comprising, a viewing medium, means for directing a lightbeam onto said medium for viewing, means responsive to beam radiationfor producing an output electrical signal, a utilization device,bistable means coupled to said means responsive to beam radiation andresponsive to said output signal to change state for controlling saidutilization device and means for driving said means for directingthrough a predetermined initial cycle to drive said bistable means intoan initial, predetermined state.
 2. Apparatus comprising, alight-transmitting medium, optical means drivable by a signal undermeasurement for projecting a beam of light onto said medium, the drivingof said optical means causing said beam to sweep said medium along apath, means located at a predetermined position on said path forproducing an output electrical signal in response to incident radiationfrom said beam, bistable means coupled to the signal-producing means andchanging state in response to said output signal, means for driving saidoptical means with a signal of predetermined magnitude sufficient todisplace said beam past said signal-producing means at least once,whereby said bistable means is caused to assume a predetermined initialstate.
 3. The apparatus as claimed in claim 2 wherein the signalproducing means comprises, two photoelectric elements spaced apart alongsaid path a distance slightly greater than the correspondingcross-sectional dimension of said beam, the region between said twoelements defining a set point for the apparatus.